Basic outline: fish farms are placed in river estuaries that are used by young wild salmon where they usually gain weight and otherwise mature before heading out to the open ocean to bulk up, return, spawn, and start the life cycle over again. The researchers claim that sea lice from the farmed fish (kept in crowded net “pens”) are decimating the young salmon before they can get to the open ocean and the estimate that the wild runs, which have already suffered a sharp decline in the study area, are headed to extinction.